1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to interface circuits operating at multiple voltages.
2. Description of the Related Art
Electronic circuits of different types have a wide variety of voltage requirements. For example, a particular type of system-on-a-chip (SOC) may operate at a particular voltage, while memory circuits and I/O devices to which it is coupled to in a system operate at different voltages. Despite these different voltages, communications between devices operating at different voltages is often required for a system to implement intended functionality. However, some circuits may be damaged if exposed to higher voltages that are used to operate other circuits.
Furthermore, on many integrated circuits (IC's) such as an SOC mentioned above, multiple voltage domains on the IC are present, despite the fact that communications between devices in the different domains is necessary. To enable communications between circuits in different voltage domains, various types of interface circuitry may be utilized. Level shifters are one type of circuit that may enable communications between two circuits residing in different voltage domains. A level shifter circuit may receive power from voltage sources in each of the power domains between which communications are to be enabled. Signals may be input into a level shifter at a first voltage (or first voltage swing) that corresponds to the operating voltage of a first voltage domain. Signals may be output from the level shifter at a second voltage (or second voltage swing) that corresponds to the operating voltage of the second voltage domain. In some cases, the input signals may have a greater voltage swing than the output signals. In other cases, the input signals may have a smaller voltage swing than the output signals.
Level shifters may be used in conjunction with driver and receiver circuits that are capable of operation within their respective voltage domains. For example, when a logic value is to be conveyed from a first voltage domain to a second, a signal conveying the logic value may be provided to a receiver in the first voltage domain and then to a level shifter. The level shifter may receive the signal in the first voltage domain and perform a level shifting operation such that the logic value it provided on a signal into the second voltage domain. A driver in the second voltage domain may receive the signal and thus drive the logic value to other circuits.